Hematopoietic stem cells (HSCs) reside in specialized bone marrow (BM) niches regulated by the sympathetic nervous system (SNS). Here, we have examined whether mononuclear phagocytes modulate the HSC niche. We defined three populations of BM mononuclear phagocytes that include Gr-1(hi) monocytes (MOs), Gr-1(lo) MOs, and macrophages (MΦ) based on differential expression of Gr-1, CD115, F4/80, and CD169. Using MO and MΦ conditional depletion models, we found that reductions in BM mononuclear phagocytes led to reduced BM CXCL12 levels, the selective down-regulation of HSC retention genes in Nestin(+) niche cells, and egress of HSCs/progenitors to the bloodstream. Furthermore, specific depletion of CD169(+) MΦ, which spares BM MOs, was sufficient to induce HSC/progenitor egress. MΦ depletion also enhanced mobilization induced by a CXCR4 antagonist or granulocyte colony-stimulating factor. These results highlight two antagonistic, tightly balanced pathways that regulate maintenance of HSCs/progenitors in the niche during homeostasis, in which MΦ cross talk with the Nestin(+) niche cell promotes retention, and in contrast, SNS signals enhance egress. Thus, strategies that target BM MΦ hold the potential to augment stem cell yields in patients that mobilize HSCs/progenitors poorly.

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Bone marrow CD169+ macrophages promote the retention of hematopoietic stem and progenitor cells in the mesenchymal stem cell niche

Human B-cell differentiation factor (BCDF) was purified to homogeneity by sequential filtration and chromatography of culture supernatants from TCL-Na1 cells on an AcA34 gel column and then on a Mono P column with fast protein liquid chromatography and reversed-phase HPLC. A 5300-fold enrichment in specific activity of BCDF with about 25% recovery was attained. The homogeneity of purified BCDF was evidenced by the following: (i) the specific activity was 1.7 X 10(7) units/mg of protein, (ii) only two bands, Mr 19,000 and 21,000, were identified by NaDodSO4/PAGE under reduced as well as nonreduced conditions, and (iii) BCDF activity was recovered from the gel after NaDodSO4/PAGE in the fractions corresponding to protein bands of Mr 19,000 or 21,000. Purified BCDF induced Ig secretion in Epstein-Barr virus-transformed cell lines; as little as 3 pM gave 50% of the maximum reaction achieved by 30-80 pM BCDF. Purified BCDF induced Ig production in activated B cells without any effect on cell growth. Purified BCDF did not show any activity of interleukin 1 or 2, B-cell stimulatory factor (BSF)p-1, B-cell growth factor II (BCGF-II), or interferon. Since BCDF was isolated and characterized as described, we propose that the BCDF that induces the final differentiation of B cells into high-rate Ig-secreting cells be designated BSFp-2.

Purification to homogeneity and characterization of human B-cell differentiation factor (BCDF or BSFp-2).

IN VERTEBRATES, four major systems of intercellular communication exist: the neural, the endocrine, the neuroendocrine, and the immune system. For many years evidence has accumulated linking the neural, the endocrine, and the neuroendocrine systems, but the immune system was often viewed as essentially autonomous. The enormous recent increase in our knowledge of how the immune system is regulated has led many scientists to postulate that this autonomy may be more apparent than real: that the immune system is subject to endocrine and neural control, and that it exerts, in turn, a reciprocal effect on neuroendocrine systems. In this review we intend to examine the interactions between the immune system and the hypothalamic-pituitary-adrenal (HPA) axis. In the first part of the review we will discuss products and components from the immune system that stimulate or inhibit the HPA axis. These include monokines and lymphokines, i.e. the regulatory secretions of the immune system, and other peptides such as ACT...

The immune-hypothalamic-pituitary-adrenal axis.

The human leukemic myeloblast HL-60 and monoblast U937 cell lines have made important contributions to the disciplines of cancer, hematology, and immunology. As sources of leukemic cells, they have been used for the study of neoplasia and therapeutics. As sources of hemic cells, they have been used for biochemical and biological analysis of regulation and differentiation in myelopoiesis. When stimulated with immunomodulatory factors, the cell lines develop properties of host-defense effector cells. They are also a source of cytokines that affect other cell types.

Human leukemic models of myelomonocytic development: a review of the HL-60 and U937 cell lines.

The most attractive properties of nanomaterials for medical and technologic applications, including their small size, large surface area, and high reactivity, are also the main factors for their potential toxicity (reviewed by Donaldson et al. 2001; Oberdorster et al. 2005). Based on inhalation studies with ambient ultrafine particles, it has been predicted that nanosized particles will have higher pulmonary deposition and biological activity compared with larger particles (reviewed by Oberdorster et al. 2005). Thus, some nanosized materials may induce not only damage at the deposition site but also distant responses as a result of their translocation and/or reactivity throughout the body (Oberdorster et al. 2005). In this respect, epidemiologic and experimental studies have suggested an association between respiratory exposure to ambient ultrafine particles (including particles with a diameter < 100 nm) and the progression of cardiovascular disease (reviewed by Brook et al. 2004).

Engineered carbon nanomaterials, including carbon nanotubes, have elicited a great deal of interest recently because of their unique electronic and mechanical properties. Single-wall carbon nanotubes (SWCNTs) have a diameter ranging from 0.7 to 1.5 nm, with lengths > 1 μm. Initial toxicologic studies demonstrated that intratracheal or pharyngeal instillation of SWCNT suspension in mice caused a persistent accumulation of carbon nanotube aggregates in the lung, followed by the rapid formation of pulmonary granulomatous and fibrotic tissues at the site (Lam et al. 2004; Shvedova et al. 2005). The unique physical characteristics and the pulmonary toxicity of SWCNTs raised concerns that respiratory exposure to these materials may be associated with systemic toxicities. In the present studies, we demonstrate that lung instillation of SWCNT is associated with a dose-dependent increase in oxidative vascular damage manifested by heme oxygenase (HO)-1 gene activation and mitochondrial alterations. Because these types of oxidative modifications are considered to play a role in atherogenesis, we further evaluated the effects of SWCNT respiratory exposure on atherosclerosis progression in ApoE−/− transgenic mice, a widely used model of human atherosclerosis.

Cardiovascular effects of pulmonary exposure to single-wall carbon nanotubes.

Lymphokine inducing "terminal differentiation" of the human monoblast leukemia line U937: a role for gamma interferon.

that Mac-1 polypeptides of 95,000 and 170,000 M, and the Mac-2 polypeptide of 32,000 M, were found in lysates of mature macrophage lines but not in other lines, including myeloid or immature leukemias The Mac-3 antigen was found in large amounts in all macrophage lines and to lesser degrees in some myeloid and B lymphoid lines The Mr of Mac-3 varied from 100,000 to 170,000, perhaps due to differential glycosylation Analysis of Mac-1 and Mac-2 antigens by flow cytometry showed expression on all macrophage lines Similarly, all three Mac antigens were detected in high amounts on macrophage lines by ‘251-labeled antibody binding Mac-1 and Mac-2 were not routinely seen on other hematopoietic lines, but Mac-3 was expressed in variably low amounts on some lines of myeloid and B cell lineage These results with macrophage lines and variants exclude a simple relationship between Mac differentiation antigens and certain macrophage characteristics (5’ nucleotidase, cytotoxic capacities, antibody-dependent phagocytosis, and production of oxygen radicals) Mac-1 and Mac-3 but not Mac-2 could be induced in the M1 myeloblast line by corticosteroid, lipopolysaccharide, and several conditioned media containing myeloid colony-stimulating activity These agents are known to induce a number of other macrophage markers in M1, eg, Fc and C receptors, phagocytosis, and lysozome production Therefore, it appears Mac-2 antigen is not required for expression of these characteristics The levels of Mac-1 and Mac-3 in M1 cells increased slowly over 6 days of stimulation, approaching those found on mature macrophage lines Although antiMac-1 does not block the detection of Mac-3 antigen on induced M1 cells, the presence of anti-Mac-1 antibody during induction partially blocked the appearance of Mac3 antigen Thus, the surface structure associated with Mac-1 antigen appears to be involved in differentiation of macrophages

Expression and induction in vitro of macrophage differentiation antigens on murine cell lines.

Human peripheral blood B cells are stimulated into proliferation by killed Staphylococcus aureus bacteria strain Cowan I (Sac). T lymphocytes in the presence of a T cell mitogen induce high numbers of immunoglobulin-secreting cells (ISC) in these Sac-stimulated B cells. The T cells can be largely replaced by a lymphokine factor. We describe here the 11000-fold purification of this B cell-inducing factor (BIF). BIF preparations that are free of IL 2 do not require IL 2 for optimal induction of ISC. This was shown by the lack of effect of IL 2 alone or with suboptimal or optimal concentrations of BIF on the induction of ISC and by the absence of IL 2 production in the purified B cell population which, with other controls, excludes significant T cell contamination. BIF, purified through four fractionation steps and free of IL 2, induces IgM, IgG, and IgA-ISC in approximately the same ratio as unfractionated lymphokine. Because we have not yet attained a pure BIF preparation, the possibility of separate factors for the production of each immunoglobulin isotype cannot be ruled out.

P. B. Litcofsky

Papers

Lymphokine inducing "terminal differentiation" of the human monoblast leukemia line U937: a role for gamma interferon.

Expression and induction in vitro of macrophage differentiation antigens on murine cell lines.

Human B cell-inducing factor(s) for production of IgM, IgG and IgA: independence from IL 2.